1. Field of the Invention
The present invention relates to knitting machines.
2. Description of the Prior Art
In circular knitting machines and other types of knitting machines, there is provided for each yarn feed, a lowering cam which acts on the butts of the needles to lower them in the active or stitch-forming stroke. There is associated with the lowering cam, which is sometimes termed the "drawdown" or "knocking-over" cam, a stop or counter-cam which faces the lowermost part of the lowering cam and which is spaced therefrom by a distance corresponding to the length of the butts in the direction of reciprocating movement of the needles.
With the increase of the speed of movement of the needles with respect to the cams, which occurs in modern machines for achieving higher production rates, serious problems arise owing to the high speed variations of the needles, operated by the above indicated cams, since the extension of the cam profiles is restricted owing to the available space in the machine and to the necessity of receiving selected needles which reach the cams at a relatively low level. Particular difficulties are encountered in the relatively sudden deceleration which the needles receive at the end of their lowering stroke imposed by the lowering cam when the needle butt contacts the stop cam. This deceleration must take place over a distance corresponding to 1 to 1.5 needle pitches, because otherwise the yarn would not be evenly drawn by the needles as too many needles and sinkers would be simultaneously in a retaining or gripping position.
In order to reduce the risk of damage to the needles due to the deceleration at the end of the needle lowering stroke, it has been proposed to provide the stop cam with an arcuate profile arranged to brake the needle gradually at the end of its lowering stroke. Hitherto, this profile of the stop cam has necessitated difficult and expensive machining of the two cams in order to obtain the required accuracy not only of the gap between the lower part of the lowering cam and the stop cam, but also between the last portion of the active profile of the lowering cam for the lowering of the needle butts and the initial portion of the stop cam profile (which must be parallel to the active profile of the lowering cam of the needle butts) and from which initial portion the aforesaid arcuate profile extends. On the other hand, it is necessary that the needle butt grazes the initial portion of the stop cam profile such that the arcuate profile of the stop cam effects deceleration of the needle according to a predetermined function or relationship.